Non-oriented electrical steel sheet and manufacturing method therefor

ABSTRACT

A non-oriented electrical steel sheet according to one embodiment of the present disclosure comprises 0.005 wt % or less of C (excluding 0 wt %), 1.0-4.0 wt % of Si, 0.15-1.5 wt % of Al, 0.1-1.0 wt % of Mn, 0.2 wt % or less of P (excluding 0 wt %), 0.005 wt % or less of N (excluding 0 wt %), 0.001-0.006 wt % of S, 0.005 wt % or less of Ti (excluding 0 wt %), and 0.005 wt % or less of O (excluding 0 wt %), and the remainder being Fe and other inevitable impurities, and satisfies formula 1 below, wherein a mean size of oxides in the precipitates is larger than a mean size of non-oxides. 
     
       
         
           
             
               
                 
                   
                     
                       
                         [ 
                         Si 
                         ] 
                       
                       1.8 
                     
                     + 
                     
                       1.3 
                       × 
                       
                         [ 
                         Al 
                         ] 
                       
                     
                   
                   &gt; 
                   
                     3.7 
                     × 
                     
                       [ 
                       Mn 
                       ] 
                     
                     × 
                     
                       [ 
                       Mn 
                       ] 
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     (Here, [Si], [Al] and [Mn] represent the contents (in wt %) of Si, Al and Mn, respectively.)

TECHNICAL FIELD

The present disclosure relates to a non-oriented electrical steel sheetand a manufacturing method therefor.

BACKGROUND ART

The non-oriented electrical steel sheets are used as core materials inrotational apparatus such as motors, generators, and stationaryapparatus such as small transformers, playing an important role indetermining the energy efficiency of electrical apparatus. Accordingly,the recent demands for energy saving and compactness of the electricapparatus emphasize improved efficiency of electrical apparatuses,subsequently demanding enhanced properties of the non-orientedelectrical steel sheets. Typical properties of electrical steel sheetare core loss and flux density. Lower core loss and higher flux densityare more desired, because the lower core loss can reduce the energy lossby heat, and the higher flux density can induce greater magnetic fieldwith the same amount of energy, when electricity is applied to the ironcore to induce a magnetic field. Accordingly, it is necessary to developa technique to manufacture a non-oriented electrical steel sheet withlow core loss and high flux density in order to cope with the increasingdemands for energy saving, environmentally friendly products.

Representative examples of the method for improving core loss, which isone of the magnetic properties of non-oriented electrical steel sheets,include a method of decreasing the thickness and a method of addingelements with high specific resistivity such as Si and Al. However, thethickness is determined by the characteristics of the product used, anddecreased thickness leads to reduced productivity and increased cost.The method of decreasing core loss by increasing the electricalresistivity of a general material by adding an alloy element having ahigh resistivity such as Si, Al, Mn or the like can reduce core loss.However, this method is contradictory in that, while it can reduce thecore loss by adding the alloying element, it inevitably results inreduction of the flux density due to the decreased saturation fluxdensity. In addition, when the Si content is 4% or more, themachinability is deteriorated, thus inhibiting the cold rolling anddecreasing the productivity. Increased Al and Mn contents can alsocontribute to the deteriorated rolling property, in which case thehardness is increased and the machinability is decreased. Accordingly,there is a need for technology to not only improve the magneticproperties, but also reduce cost by way of adding these additiveelements in most appropriate proportion.

Meanwhile, there are unavoidable impurities added in the steel such asC, S, N, O, Ti, or the like, and these are combined with the additiveelements such as Fe, SI, Al, Mn, or the like, to form fine precipitatesthat suppress the grain growth and interfere with the migration of themagnetic domains, thus deteriorating the magnetic properties. Suchprecipitates in steel include carbide, nitride, sulfide, oxide, and thelike. These appear individually or in combination. These fine compoundsare classified as dross or precipitates according to their size andcause of formation, and it is believed that the dross more than 100 nmin size does not significantly affect the grain growth, while theprecipitates that are below 100 nm in size particularly inhibit thegrain growth.

When the precipitates are small in size, the quantity of precipitatesincreases and contribute to suppressing the migration of the magneticdomains or grain growth, and accordingly, it is important to increasethe size of the precipitates or to make a composite of two or moreprecipitates.

DISCLOSURE Technical Problem

The present invention has been made in an effort to provide anon-oriented electrical steel sheet with improved magnetic properties byfacilitating migration of magnetic domains during grain growth andmagnetization by way of limiting the amounts of added alloy elements andallowing the precipitates to grow to a larger size, and a manufacturingmethod therefor.

Technical Solution

The non-oriented electrical steel sheet according to one embodiment ofthe present disclosure includes 0.005 wt % or less of C (excluding 0 wt%), 1.0-4.0 wt % of Si, 0.15-1.5 wt % of Al, 0.1-1.0 wt % of Mn, 0.2 orof P (excluding 0 wt %), 0.005 wt % or less of N (excluding 0 wt %),0.001-0.006 wt % of S, 0.005 wt % or less of Ti (excluding 0 wt %), and0.005 wt % or less of O (excluding 0 wt %), and the remainder being Feand other inevitable impurities, and satisfies formula 1 below, whereina mean size of oxides in the precipitates is larger than a mean size ofnon-oxides.

$\begin{matrix}{{\frac{\lbrack{Si}\rbrack}{1.8} + {1.3 \times \lbrack{Al}\rbrack}} > {3.7 \times \lbrack{Mn}\rbrack \times \lbrack{Mn}\rbrack}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

(Here, [Si], [Al] and [Mn] represent the contents (in wt %) of Si, Aland Mn, respectively.)

The number of oxides in the precipitates may be larger than that ofnon-oxides.

0.01 to 0.2 wt % of Sn and Sb may be further included, individually orin combination, respectively.

The number of FeO in the precipitates or precipitates containing FeO maybe 40% or more.

The mean particle size may be between 50 and 180 μm.

A manufacturing method for a non-oriented electrical steel sheetaccording to one embodiment of the present disclosure includes steps of:heating a slab including 0.005 wt % or less of C (excluding 0 wt %),1.0-4.0 wt % of Si, 0.15-1.5 wt % of Al, 0.1-1.0 wt % of Mn, 0.2 wt % orless of P (excluding 0 wt %), 0.005 wt % or less of N (excluding 0 wt%), 0.001-0.006 wt % of S, 0.005 wt % or less of Ti (excluding 0 wt %),and 0.005 wt % or less of O (excluding 0 wt %), and the remainder beingFe and other inevitable impurities, and satisfying formula 1 below, andhot rolling the slab to prepare a hot rolled sheet; winding and coolingthe hot rolled sheet; annealing and cooling the hot rolled sheet; coldrolling the hot rolled annealing sheet to prepare a cold rolled sheet;and final annealing and then cooling the cold rolled sheet, in which inthe step of winding and cooling the hot rolled sheet includes cooling at600° C. or higher for 30 minutes or more, the step of annealing and thencooling the hot rolled sheet includes cooling at 600° C. or higher for 5seconds or more, and the step of final annealing and then cooling thecold rolled sheet includes cooling at 600° C. or higher for 5 seconds ormore.

$\begin{matrix}{{\frac{\lbrack{Si}\rbrack}{1.8} + {1.3 \times \lbrack{Al}\rbrack}} > {3.7 \times \lbrack{Mn}\rbrack \times \lbrack{Mn}\rbrack}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

(Here, [Si], [Al] and [Mn] represent the contents (in wt %) of Si, Aland Mn, respectively.)

The slab may further include 0.01 to 0.2 wt % of Sn and Sb, individuallyor in combination.

The step of preparing a hot rolled sheet may include heating the slab at1200° C. or less.

The temperature of the winding may be 600 to 800° C. in the step ofwinding and cooling the hot rolled sheet.

The temperature of the hot rolled sheet annealing may be 850 to 1150° C.in the step of annealing and then cooling the hot rolled sheet.

The step of cold rolling the hot rolled annealing sheet to prepare coldrolled sheet may include cold rolling the sheet to a thickness of 0.1 to0.7 mm.

In the step of cold rolling the hot rolled annealing sheet to prepare acold rolled sheet, the cold rolling may include primary cold rolling,intermediate annealing, and secondary cold rolling.

For annealing of the step of final annealing and then cooling the coldrolled sheet, the cracking temperature of the annealing may be 850 to1100° C.

A mean size of oxides in the precipitates of the manufactured electricalsteel sheets may be larger than a mean size of non-oxides.

The number of oxides in the precipitates may be larger than that ofnon-oxides.

The number of FeO in the precipitates or precipitates containing FeO maybe 40% or more.

The mean particle size may be between 50 and 180 μm.

Advantageous Effects

The non-oriented electrical steel sheet according to one embodiment ofthe present disclosure can improve the magnetic properties by allowingthe precipitates to grow to a larger size, thereby facilitating graingrowth and migration of magnetic domains during magnetization.

MODE FOR INVENTION

The terms “first”, “second” and “third” as used herein are intended todescribe various parts, components, regions, layers and/or sections, butnot construed as limiting. These terms are merely used to distinguishany parts, components, regions, layers and/or sections from anotherparts, components, regions, layers and/or sections. Accordingly, a firstpart, component, region, layer or section to be described below may bereferred to as a second part, component, region, layer or sectionwithout departing from the scope of the present disclosure.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to limit the present disclosure.The singular forms used herein include plural forms as long as thephrases do not expressly mean to the contrary. As used herein, themeaning of “comprising” specifies specific features, regions, integers,steps, operations, elements and/or components, and does not exclude thepresence or the addition of other features, regions, integers, steps,operations, elements and/or components.

When a portion is referred to as being “above” or “on” another portion,it may be directly on another portion or may be accompanied by yetanother portion disposed in between. In contrast, when a portion isreferred to as being “directly above” another portion, no other portionis interposed in between.

Unless otherwise defined, all terms including technical and scientificterms used herein have the same meaning as commonly understood by thosewith ordinary knowledge in the art to which this invention belongs.Terms defined in the general dictionaries are not to be construed as theideal or very formal meanings unless they are further interpreted anddefined as having a meaning consistent with the relevant technicalliterature and the present disclosure.

In addition, unless otherwise stated, % means wt %, and 1 ppm is 0.0001wt %.

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail to help those with ordinary knowledge in the arteasily achieve the present disclosure. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention.

The non-oriented electrical steel sheet according to one embodiment ofthe present disclosure includes 0.005 wt % or less of C (excluding 0 wt%), 1.0-4.0 wt % of Si, 0.15-1.5 wt % of Al, 0.1-1.0 wt % of Mn, 0.2 wt% or less of P (excluding 0 wt %), 0.005 wt % or less of N (excluding 0wt %), 0.001-0.006 wt % of S, 0.005 wt % or less of Ti (excluding 0 wt%), and 0.005 wt % or less of O (excluding 0 wt %), and the remainderbeing Fe and other inevitable impurities, and satisfies formula 1 below,wherein a mean size of oxides in the precipitates is larger than a meansize of non-oxides.

$\begin{matrix}{{\frac{\lbrack{Si}\rbrack}{1.8} + {1.3 \times \lbrack{Al}\rbrack}} > {3.7 \times \lbrack{Mn}\rbrack \times \lbrack{Mn}\rbrack}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

(Here, [Si], [Al] and [Mn] represent the contents (in wt %) of Si, Aland Mn, respectively.)

In one embodiment of the present invention, among the components of thenon-oriented electrical steel sheet, particular components such as Si,Al and Mn were precisely regulated to produce precipitates as large aspossible, and also to cause the precipitates to precipitate in a largersize by being in combination with each other, rather than existingindividually. In addition, a mean size of oxides in the precipitates isformed larger than a mean size of the non-oxide, to improve the magneticproperties.

In one embodiment of the present disclosure, the elements being addedare Si, Mn, Al, P or, if necessary, Sn and Sb, and Fe in the basematerial. Other added elements are O, C, N, S, and so on, which need tobe managed at a low content. Among these, element such as N or C formsnitrides and carbides with other elements, element such as Al, Mn, Si,Fe, and the like forms oxides with O, and element such as Mn and Cu formsulfides, and the like with S, all of which are formed individually orin combination.

In one embodiment of the present disclosure, the precipitates werecoarsened, and in particular, the precipitates were precipitated incombination, rather than alone, to further facilitate the growth. Amongthem, oxide is more easily coarsened, since coarsening the oxide ispossible without adding additive elements. As a result, it was confirmedthat the magnetic properties of the electrical steel sheet wereimproved.

In one embodiment of the present invention, the oxide was 50% or more ofthe total number of precipitates in the precipitates, and in the oxides,FeO in particular accounted for more than 40%. In particular, theinfluence of oxides greatly contributed to the formation of the complexprecipitates. These oxides are considered to be O remaining as oxides insteels after O was lowered in the steelmaking process, or precipitatedafter annealing. Sulfide was precipitated in a large amount whenreheating slabs and cooling after hot rolling, which appeared as CuS,MnS or complex precipitates of these. However, the oxide has morecomplex precipitates of oxides such as FeO, Al₂O₂, and than those ofsulfides, and the bonding of the oxide with the nitride and the carbideis relatively less.

In one embodiment of the present disclosure, the oxides in theprecipitates were present individually or in combination, and observedin a mean size of 15 nm to 70 nm and an average quantity of 10,000 to400,000 precipitates per 1 mm². In addition, the non-oxides in theprecipitates were present individually or in combination and observed ina mean size of 10 nm to 50 nm and an average quantity of 5,000 to200,000 precipitates per 1 mm².

Since the oxides are formed in the precipitates with a larger mean sizethan that of the non-oxides, the grain growth is facilitated, andspecifically, the mean particle size of 50 to 180 μm can be achieved.The ‘particle size’ as used herein refers to the particle size measuredby the intercept method commonly used in the field of the electricalsteel sheets.

The reason for limiting the components of the non-oriented electricalsteel sheet will be described below.

Si: 1.0-4.0 wt %

Silicon (Si) is a major additive element for it is the component thatincreases the specific resistivity of steel to lower the core loss, thatis, the eddy current loss. Si is an element that easily forms oxide.When Si is added in an insufficient amount, it is difficult to obtainlow core loss properties, and Si added in an excessive amount can hindercold rolling. Accordingly, Si may be limited to 1.0-4.0 wt %.

Mn: 0.1-1.0 wt %

Like Si or Al, manganese (Mn) has an effect of increasing specificresistivity that lowers core loss, and accordingly, Mn is added in anamount of 0.1 wt % or more to improve core loss. However, increasedamount of Mn causes reduced saturation flux density which in turnresults in reduced flux density. In addition, Mn is combined with S toform the fine MnS precipitates, which inhibit grain growth and hinderthe magnetic domain wall movement, thus increasing core loss, or moreparticularly, increasing the hysteresis loss. Accordingly, Mn is addedin an amount of 1.0 wt % or less.

Al: 0.15-1.5 wt %

Aluminum (Al) is an element that is inevitably added for steeldeoxidation in a steelmaking process, and because Al is a major elementthat increases the specific resistivity, in many cases, Al is added tolower the core loss. However, when added, Al also serves to reduce thesaturation flux density. In addition, the presence of considerablyinsufficient Al content can cause formation of fine AlN, which mayinhibit the grain growth and result in deteriorated magnetic properties.In addition, the presence of too much Al can serve as a cause ofdecreased flux density. Accordingly, the content of Al may be limited to0.15-1.5 wt %.

P: 0.2 wt % or Less

Phosphorus (P) increases the specific resistivity to decrease the coreloss, and segregated on the grain boundaries to inhibit the formation oftexture detrimental to the magnetic properties, while forming afavorable texture {100}. However, if added in an overly large amount, Pcan deteriorate rolling property. Accordingly, P may be limited to 0.2wt % or less.

C: 0.005 wt % or Less

When added in an overly large amount, carbon (C) increases the austeniteregion, increases the phase transformation interval, and inhibits thegrain growth of ferrite during annealing, thus resulting in increasedcore loss. Further, C also binds with Ti, or the like to form carbidesthat deteriorate magnetic properties, and it increases core loss bymagnetism aging as it is processed and used in the final product such aselectrical product. Accordingly, C may be limited to 0.005 wt % or less.

N: 0.005 wt % or Less

Nitrogen (N) is an element detrimental to the magnetic properties,because N binds strongly with Al, Ti, or the like to form nitrides toinhibit the grain growth, and so on. Accordingly, content of N ispreferably maintained at a low level and may be limited to 0.005 wt % orless.

S: 0.001-0.006 wt %

Sulfur (S) is an element that forms sulfides such as MnS, CuS and (Cu,Mn)S, which are harmful to magnetic properties. Accordingly, the contentof S is preferably maintained as low as possible. However, aconsiderably insufficient amount of S can be rather disadvantageous tothe texture formation and result in deteriorated magnetic properties. Inaddition, the presence of overly large amount of S can causedeteriorated magnetic properties due to increasing presence of finesulfides. Accordingly, S may be limited to 0.001-0.006 wt %.

Ti: 0.005 wt % or Less

Titanium (Ti) forms fine carbides and nitrides to inhibit the graingrowth. An increased content of Ti causes increased presence of finecarbides and nitrides which deteriorate the texture and result indeteriorated magnetic properties. Accordingly, Ti may be limited to0.005 wt % or less.

O: 0.005 wt % or Less

Content of oxygen (O) may be maintained as low as possible because Oforms various oxides that will inhibit grain growth. Accordingly, O maybe limited to 0.005 wt % or less.

Sn, Sb: 0.01 to 0.2 wt %

As the segregating elements in the grain boundaries, tin (Sn) andantimony (Sb) suppress the spreading of nitrogen through the grainboundaries and suppress the {111} texture which is detrimental to themagnetic properties. Sn and Sb are added to increase favorable {100}texture and improve the magnetic properties. If Sn or Sb, eitherindividually or in combination, is present in an overly large amount, itmay inhibit the grain growth, which will deteriorate the magneticproperties and the rolling properties. Accordingly, when Sn or Sb isadded, the content of Sn and Sb, either individually or in combination,may be limited to 0.01 to 0.2 wt %.

In particular, in one embodiment of the present disclosure, the amountsof Si, Mn, and Al are regulated to satisfy formula 1 below in order toensure that there is not a high amount of Mn, but a high amount of Si,and with the presence of a substantial amount of Al, to suppress AlN,and the like.

$\begin{matrix}{{\frac{\lbrack{Si}\rbrack}{1.8} + {1.3 \times \lbrack{Al}\rbrack}} > {3.7 \times \lbrack{Mn}\rbrack \times \lbrack{Mn}\rbrack}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

(Here, [Si], [Al] and [Mn] represent the contents (in wt %) of Si, Aland Mn, respectively.)

A manufacturing method for a non-oriented electrical steel sheetaccording to one embodiment of the present disclosure includes steps of:heating a slab including 0.005 wt % or less of C (excluding 0 wt %),1.0-4.0 wt % of Si, 0.15-1.5 wt % of Al, 0.1-1.0 wt % of Mn, 0.2 wt % orless of P (excluding 0 wt %), 0.005 wt % or less of N (excluding 0 wt%), 0.001-0.006 wt % of S, 0.005 wt % or less of Ti (excluding 0 wt %),and 0.005 wt % or less of O (excluding 0 wt %), and the remainder beingFe and other inevitable impurities, and satisfying formula 1 below, andhot rolling the slab to prepare a hot rolled sheet; winding and coolingthe hot rolled sheet; annealing and cooling the hot rolled sheet; coldrolling the hot rolled annealing sheet to prepare a cold rolled sheet;and final annealing and then cooling the cold rolled sheet, in which inthe step of winding and cooling the hot rolled sheet includes cooling at600° C. or higher for 30 minutes or more, the step of annealing and thencooling the hot rolled sheet includes cooling at 600° C. or higher for 5seconds or more, and the step of final annealing and then cooling thecold rolled sheet includes cooling at 600° C. or higher for 5 seconds ormore.

In one embodiment of the present disclosure, after preparing the hotrolled sheet, after annealing the hot rolled sheet, and after annealingthe cold rolled sheet, cooling is performed slowly to allow time for theprecipitates to grow, thereby improving the magnetic properties.

Hereinafter, the process will be described step by step.

First, the slab is heated and then hot rolled to prepare a hot rolledsheet. The reason for limiting the addition ratio of each composition isthe same as the reason for limiting the addition ratio of thenon-oriented electrical steel sheet described above. Since thecomposition of the slab does not substantially change during hotrolling, hot rolled sheet annealing, cold rolling, and final annealing,and the like, the composition of the slab is substantially the same asthat of the non-oriented electrical steel sheet.

The slab may be charged to a furnace and heated at 1200° C. or less.When heated at an overly high heating temperature, precipitates such asAlN and MnS present in the slab can be re-solved and then formed intofine precipitates during hot rolling, which may inhibit the grain growthand deteriorate the magnetic properties. More specifically, the slab maybe heated at 1050° C. to 1200° C.

The heated slab is hot rolled to 1.4 mm to 3 mm to prepare a hot rolledsheet. During hot rolling, the finishing rolling of the finishingmilling is completed in the ferrite phase, with the final reduction rateof 20% or less for the purpose of sheet shape control.

Next, the hot rolled sheet is wound and then cooled. The hot rolledsheet is wound at a temperature of 600° C. to 800° C. and then cooled inair or in a separate furnace. The temperature for cooling is allowed tobe maintained at 600° C. or higher for at least 30 minutes or more. Ifthe temperature is too low or the time is kept short, growth ofprecipitates may be difficult and fine precipitates may appear. Morespecifically, the temperature may be maintained between 600 and 800° C.for 30 minutes to 3 hours.

Next, the hot rolled sheet is annealed and cooled. The hot rolled sheetis annealed to improve the magnetic properties, and hot rolled sheetannealing temperature is 850 to 1150° C. If the hot rolled sheetannealing temperature is too low, the grain growth may be insufficient.If the hot rolled sheet annealing temperature is too high, there may beexcessive grain growth, which may cause excessive surface defects.

For cooling after hot rolled sheet annealing, cooling is not quenched,but maintained at 600° C. or higher for 5 seconds or more. If thetemperature is too low or the sustaining time is short during cooling,it may be difficult to coarsen precipitates and the sheet may be bent.More specifically, the cooling temperature may be from 600 to 800 ° C.,and may be maintained for 5 to 30 seconds.

The hot rolled sheet may be pickled after annealing.

Next, the hot rolled annealing sheet is cold rolled to prepare a coldrolled sheet. The cold rolling may finally roll to a thickness of 0.1 mmto 0.7 mm and may include primary cold rolling, intermediate annealingand secondary cold rolling as necessary, with the final reduction ratiobeing in the range of 50 to 95%.

Next, the cold rolled sheet is finally annealed and then cooled. Duringannealing in a cold rolled sheet annealing process, the crackingtemperature of the annealing is 850 to 1100° C. When the cold rolledsheet annealing temperature is 850° C. or lower, insufficient graingrowth results in increased {111} texture that is detrimental to themagnetic properties. When the cold rolled sheet annealing temperature is1100° C. or higher, the excessive grain growth can adversely affect themagnetic properties. Accordingly, the cracking temperature of the coldrolled sheet is set at 850 to 1100° C.

For cooling after cold rolled sheet annealing, cooling is not quenched,but maintained at 600° C. or higher for 5 seconds or more. If thetemperature is too low or the sustaining time is short during cooling,the fine precipitates can individually appear. More specifically, thecooling temperature may be from 600 to 800° C., and may be maintainedfor 5 to 30 seconds.

The annealing sheet is shipped to customer after insulation coatingtreatment. The insulating coating may be treated with an organic,inorganic or organic-inorganic composite coating, or may be treated withother coating agents capable of insulation. The customer may use thesteel sheet as it is after processing it.

Hereinafter, the present disclosure is explained in more detail withreference to Examples. However, the Examples are described merely toillustrate the present disclosure, and the present disclosure is notlimited thereto.

EXAMPLE 1

A steel ingot was prepared with the compositions shown in Tables 1 and 2below, from which inventive steels A1 to A7 including Si, Al and Mncontents (in wt %) satisfying formula 1, and comparative steels A8 toA12 including Si, Al and Mn contents (in wt %) not satisfying formula 1were melted by vacuum melting.

Vacuum melt steels A1 to A7 were prepared by including Si, Al, and Mn inthe range of the present disclosure, after which each steel ingot washeated at 1120° C., hot rolled to a thickness of 2.2 mm, and wound, andthen slowly cooled in the air and wound as shown in Table 2. The cooledhot rolled steel sheet was then annealed in a nitrogen atmosphere for 5minutes, followed by slow cooling at a temperature of 600° C. or higherin an atmosphere in which nitrogen and oxygen were mixed, and thenfinally quenched by spraying water. The annealed hot rolled sheets werepickled and then cold rolled to 0.35 mm thickness and for the finalannealing, the cold rolled sheet was annealed for 2 minutes in a 30%hydrogen and 70% nitrogen mixed atmosphere. The cooling bed was cooledat atmosphere of the 40% hydrogen and nitrogen. The final annealingsheet was examined for the size and quantity of oxides, sulfides,carbides, nitrides and their complex precipitates for each specimen andthe grains and magnetic properties were measured and listed in Table 3below.

As a method to analyze the size, type and distribution of precipitates,carbon replica extracted from specimen was observed by TEM and analyzedby EDS. The TEM observation was carried out by analyzing the type ofprecipitates through the EDS spectrum on the randomly selected areaswithout bias.

Core loss (W_(15/50)) was measured as the average loss (W/kg), in therolling direction and the perpendicular direction to the rollingdirection, when flux density of 1.5 Tesla was induced at 50 Hzfrequency.

The flux density (B₅₀) was measured by the magnitude of flux density(Tesla) induced when a magnetic field of 5000 Nm was applied.

TABLE 1 Item C: Si: Al: Mn: P S N Ti Sn Sb A1 0.0025 1.56 0.25 0.420.031 0.0024 0.0014 0.0002 0.026 0.012 A2 0.0028 2.64 0.22 0.4 0.0360.0021 0.0021 0.0015 0.019 0 A3 0.0025 2.82 0.82 0.8 0.045 0.0028 0.00140.0017 0 0 A4 0.0022 2.95 0.78 0.62 0.055 0.0021 0.0012 0.0016 0 0 A50.0025 2.82 1.3 0.45 0.032 0.0015 0.0025 0.0011 0 0.031 A6 0.0028 2.910.32 0.52 0.031 0.0018 0.0021 0.0011 0.024 0.021 A7 0.0022 3.3 0.25 0.40.035 0.0032 0.0026 0.0015 0.036 0.015 A8 0.0021 0.52 0.002 0.45 0.0310.0024 0.0014 0.0002 0.026 0.012 A9 0.0026 1.43 0.25 0.62 0.045 0.00010.0015 0.0019 0.025 0.031 A10 0.0023 2.24 0.12 0.72 0.055 0.0032 0.00180.0021 0 0.019 A11 0.0027 2.51 0.45 0.9 0.023 0.0035 0.0021 0.0021 0.0350 A12 0.0029 2.96 0.74 1.3 0.019 0.0019 0.0019 0.0025 0.043 0

TABLE 2 Hot rolled sheet anneal Cold rolled sheet anneal SustainingSustaining Cooling after winding Anneal time (sec) at Anneal time (sec)at Steel Satisfy Temp. Time temp. 600° C. or temp. 600° C. or gradeFormula 1 (° C.) (min) (° C.) higher (° C.) higher Remarks A1 ◯ 700 60900 10 900 8 Inventive steel 1 A2 ◯ 650 60 1000 12 1030 15 Inventivesteel 2 A3 ◯ 650 60 1000 10 1030 15 Inventive steel 3 A4 ◯ 650 60 1000 71030 15 Inventive steel 4 A5 ◯ 650 60 1000 7 1050 15 Inventive steel 5A6 ◯ 650 60 1000 10 1050 15 Inventive steel 6 A7 ◯ 650 60 1000 10 105015 Inventive steel 7 A8 X 700 60 900 10 900 8 Comp. steel 1 A9 X 700 60900 12 900 8 Comp. steel 2 A10 X 650 60 1000 12 1050 15 Comp. steel 3A11 X 650 60 1000 12 1050 15 Comp. steel 4 A12 X 650 60 1000 12 1050 15Comp. steel 5

TABLE 3 Oxide in Non-oxide in Core Flux Particle precipitate FeO ratioprecipitate loss density Steel size Size Ratio (%) in Size Ratio(W_(15/50)) B₅₀ grade (μm) (nm) (%) precipitate (nm) (%) W/kg TeslaRemarks A1 60 45 55 45 40 45 3.72 1.78 Inventive steel 1 A2 80 48 60 5043 40 2.21 1.73 Inventive steel 2 A3 87 60 62 54 45 38 2.12 1.71Inventive steel 3 A4 120 65 65 48 46 35 1.85 1.69 Inventive steel 4 A5120 58 70 55 45 30 1.92 1.68 Inventive steel 5 A6 110 45 72 62 40 281.95 169 Inventive steel 6 A7 160 48 70 55 35 30 1.93 1.68 Inventivesteel 7 A8 40 32 35 28 38 65 6.43 1.71 Comp. steel 1 A9 45 33 40 35 3860 4.52 1.69 Comp. steel 2 A10 60 31 35 32 37 65 2.52 1.66 Comp. steel 3A11 65 22 40 36 39 60 2.54 1.65 Comp. steel 4 A12 70 28 45 30 35 55 2.321.62 Comp. steel 5

As shown in Table 1 to Table 3, it can be seen that A1 to A7 satisfy thecomposition ranges of the electrical steel sheet and formula 1, the sizeof the oxide in the precipitates is larger than the size of thenon-oxide, the grain growth is good, and the core loss and flux densityare also excellent. On the other hand, it can be seen that A8 to A12 donot satisfy the composition ranges of the electrical steel sheet andformula 1, and some of these exhibit the size of the oxides smaller thanthe size of the non-oxide in the precipitates. Accordingly, it isapparent that the core loss and the flux density are inferior.

EXAMPLE 2

A steel ingot was prepared with the compositions shown in Tables 4 and 5below, from which inventive steels A13 to A15 including Si, Al and Mncontents (in wt %) satisfying formula 1 were melted by vacuum melting.

Each steel ingot was heated at 1120° C., hot rolled to a thickness of2.2 mm, and wound, and then slowly cooled in the air and wound as shownin Table 5. The cooled hot rolled steel sheet was then annealed in anitrogen atmosphere for 5 minutes, followed by slow cooling at atemperature of 600° C. or higher in an atmosphere in which nitrogen andoxygen were mixed, and then finally quenched by spraying water. Theannealed hot rolled sheets were pickled and then cold rolled to 0.35 mmthickness and for the final annealing, the cold rolled sheet wasannealed for 2 minutes in a 30% hydrogen and 70% nitrogen mixedatmosphere. The cooling bed was cooled at atmosphere of the 40% hydrogenand nitrogen. The final annealing sheet was examined for the size andamount of oxides, sulfides, carbides, nitrides and their complexprecipitates for each specimen and the grains and magnetic propertieswere measured and listed in Table 6 below.

TABLE 4 Item C Si Al Mn P S N Ti Sn Sb A13 0.0035 2.12 0.31 0.2 0.0320.0044 0.0025 0.0013 0 0.035 A14 0.0024 2.52 0.26 0.21 0.043 0.00220.0029 0.0011 0.041 0 A15 0.0021 3.12 0.51 0.8 0.045 0.0045 0.00220.0009 0.031 0

TABLE 5 Hot rolled sheet anneal Cold rolled sheet anneal & cool & coolSustaining Sustaining Cooling after winding Anneal time (sec) Annealtime at Steel Satisfy Temp. Time temp at 600° C. temp 600° C. gradeFormula 1 (° C.) (min) (° C.) or higher (° C.) or higher Remarks A13 ◯650 50 950 12 980 10 Inventive steel 8 A13 ◯ 650 50 800 2 980 2 Comp.steel 6 A14 ◯ 620 80 1020 10 1020 11 Inventive steel 9 A14 ◯ 620 80 10202 1020 11 Comp. steel 7 A14 ◯ 620 1 1020 2 900 2 Comp. steel 8 A14 ◯ 52080 1020 2 1020 2 Comp. steel 9 A15 ◯ 650 30 1020 15 1020 12 Inventivesteel 10 A15 ◯ 650 1 1020 2 1020 2 Comp. steel 10 A15 ◯ 650 30 1020 21020 2 Comp. steel 11

TABLE 6 Oxide in Non-oxide in Core Flux Particie precipitate FeO ratioprecipitate loss density Steel size Size Ratio (%) in Size Ratio(W_(15/50)) B₅₀ grade (μm) (nm) (%) precipitate (nm) (%) W/kg TeslaRemarks A13 75 47 68 52 35 32 2.81 1.75 Inventive steel 8 A13 45 30 4135 38 59 3.52 1.72 Comp. steel 6 A14 78 52 65 45 46 35 2.23 1.71Inventive steel 9 A14 60 28 38 38 35 62 2.52 1.68 Comp. steel 7 A14 4031 35 35 35 65 2.43 1.67 Comp. steel 8 A14 60 28 36 32 36 64 2.61 1.68Comp. steel 9 A15 120 65 80 57 38 20 2.11 1.71 Inventive steel 10 A15 7225 45 35 33 55 2.43 1.65 Comp. steel 10 A15 67 21 42 36 33 58 2.64 1.63Comp. steel 11

As shown in Tables 4 to 6, it can be seen that the inventive steel wasgiven enough cooling time after winding compared to comparative steel,and also given sufficient time at 600° C. or higher after annealing ofthe hot rolled sheet and the cold rolled sheet. Accordingly, oxidesincluding FeO oxides were well formed, resulting in the good graingrowth and excellent magnetic properties.

On the other hand, comparative steel 6 was subjected to a low hot rolledsheet annealing temperature, and during cooling, maintained for a shortsustaining time at a temperature of 600° C. or higher, which resulted insmall oxide size in precipitates and also small oxide amount inprecipitates. Comparative steel 7 was also subjected to cooling for ashort cooling time after the hot rolled sheet annealing, thus resultingin relatively smaller oxide size than that of the non-oxides in theprecipitates, and also in smaller quantity, and the FeO oxide ratio wasalso low as 40% or less. Comparative steel 8 was cooled rapidly by watercooling after winding and subjected to cooling at 600° C. or higherafter the hot rolled sheet annealing for a short cooling time, and alsoto a short cooling after the cold rolled sheet annealing, which resultedin the insufficient formation of oxides including FeO in theprecipitates. As a result, core loss was relatively high and fluxdensity was low. It can be seen that comparative steel 9, whichsatisfies the composition, but has a low winding temperature and shortannealing time during cooling after the hot rolled sheet annealing,exhibited small oxide such as FeO or small complex precipitates, and thenumber of the oxides was also smaller as compared with that ofnon-oxides, which resulted in small particle size and inferior magneticproperties. It can be seen that comparative steel 10 as well as thecomparative steel 11 was quenched in water after winding and given ashort cooling time after the hot rolled (and cold rolled) sheetannealing, which resulted in a low FeO ratio in the precipitates andinsufficient formation of oxides. As a result, the grains were small andthe magnetic properties were insufficient.

It will be understood that the present disclosure is not limited to theabove embodiments but may be embodied in many different forms from eachother and those of ordinary skill in the art to which the presentdisclosure pertains can implement the invention in other specific formswithout changing the technical idea or essential features of the presentdisclosure. Accordingly, it will be understood that the exemplaryembodiments described above are only illustrative, and should not beconstrued as limiting.

1. A non-oriented electrical steel sheet, comprising: 0.005 wt % or lessof C (excluding 0 wt %), 1.0-4.0 wt % of Si, 0.15-1.5 wt % of Al,0.1-1.0 wt % of Mn, 0.2 wt % or less of P (excluding 0 wt %), 0.005 wt %or less of N (excluding 0 wt %), 0.001-0.006 wt % of S, 0.005 wt % orless of Ti (excluding 0 wt %), and 0.005 wt % or less of O (excluding 0wt %), and the remainder being Fe and other inevitable impurities, andsatisfies formula 1 below, wherein a mean size of oxides in theprecipitates is larger than a mean size of non-oxides. $\begin{matrix}{{\frac{\lbrack{Si}\rbrack}{1.8} + {1.3 \times \lbrack{Al}\rbrack}} > {3.7 \times \lbrack{Mn}\rbrack \times \lbrack{Mn}\rbrack}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$ (Here, [Si], [Al] and [Mn] represent the contents (in wt%) of Si, Al and Mn, respectively.)
 2. The non-oriented electrical steelsheet of claim 1, wherein a number of oxides in the precipitates islarger than that of non-oxides.
 3. The non-oriented electrical steelsheet of claim 1, further comprising 0.01 to 0.2 wt % of Sn and Sb,individually or in combination, respectively.
 4. The non-orientedelectrical steel sheet of claim 1, wherein a number of FeO in theprecipitates or precipitates containing FeO is 40% or more.
 5. Thenon-oriented electrical steel sheet of claim 1, wherein a mean particlesize is 50 to 180 μm.
 6. A method for manufacturing a non-orientedelectrical steel sheet, comprising steps of: heating a slab comprising0.005 wt % or less of C (excluding 0 wt %), 1.0-4.0 wt % of Si, 0.15-1.5wt % of Al, 0.1-1.0 wt % of Mn, 0.2 wt % or less of P (excluding 0 wt%), 0.005 wt % or less of N (excluding 0 wt %), 0.001-0.006 wt % of S,0.005 wt % or less of Ti (excluding 0 wt %), and 0.005 wt % or less of O(excluding 0 wt %), and the remainder being Fe and other inevitableimpurities, and satisfying formula 1 below and then hot rolling the slabto prepare a hot rolled sheet; winding and then cooling the hot rolledsheet; annealing and then cooling the hot rolled sheet; cold rolling thehot rolled annealing sheet to prepare a cold rolled sheet; and finalannealing and then cooling the cold rolled sheet, wherein, the step ofwinding and cooling the hot rolled sheet comprises cooling at 600° C. orhigher for 30 minutes or more, the step of annealing and then coolingthe hot rolled sheet includes cooling at 600° C. or higher for 5 secondsor more, and the step of annealing and then cooling the cold rolledsheet includes cooling at 600° C. or higher for 5 seconds or more.$\begin{matrix}{{\frac{\lbrack{Si}\rbrack}{1.8} + {1.3 \times \lbrack{Al}\rbrack}} > {3.7 \times \lbrack{Mn}\rbrack \times \lbrack{Mn}\rbrack}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$ (Here, [Si], [Al] and [Mn] represent the contents (in wt%) of Si, Al and Mn, respectively.)
 7. The method of claim 6, whereinwherein the slab further comprises 0.01 to 0.2 wt % of Sn and Sb,individually or in combination.
 8. The method of claim 6, wherein thestep of preparing the hot rolled sheet comprises heating the slab at1200° C. or lower.
 9. The method of claim 6, wherein a temperature ofthe winding is 600 to 800° C. in the step of winding and then coolingthe hot rolled sheet.
 10. The method of claim 6, wherein a temperatureof the hot rolled sheet annealing is 850 to 1150° C. in the step ofannealing and then cooling the hot rolled sheet.
 11. The method of claim6, wherein wherein the step of cold rolling the hot rolled annealingsheet to prepare a cold rolled sheet comprises cold rolling to athickness of 0.1 to 0.7 mm.
 12. The method of claim 6, wherein the stepof cold rolling the hot rolled annealing sheet to prepare a cold rolledsheet comprises primary cold rolling, intermediate annealing, andsecondary cold rolling.
 13. The method of claim 6, wherein a crackingtemperature of the cold rolled sheet annealing during annealing is 850to 1100° C. in the step of annealing and then cooling the cold rolledsheet.
 14. The method of claim 6, wherein a mean size of oxides in theprecipitates of a manufactured electrical steel sheet is larger than amean size of non-oxides.
 15. The method of claim 14, wherein a number ofoxides in the precipitates is larger than that of non-oxides.
 16. Themethod of claim 14, wherein a number of FeO in the precipitates orprecipitates containing FeO is 40% or more.
 17. The method of claim 14,wherein a mean particle size is 50 to 180 μm.